The present invention relates to a printed circuit board assembly, especially to a printed circuit board assembly wherein the printed circuit board stably contacts with a circuit membrane and can be used for keyboards and scanners.
As computer becomes more and more important and omnipresent to modern society, people rely on keyboard to key in various data for computer or cash register. Therefore, the keyboards are under extensive research and the requirement for keyboards are strict. For example, the appearance, tactility, click sound and balance of the keyboards are demanding factors.
The conventional keyboard generally comprises a printed circuit board assembled with a circuit membrane. The circuit membrane is a silvery mesh film with extended ribbon cable connected to the rigid printed circuit board provides electrical connection between the printed circuit board and the circuit membrane.
FIG. 1 shows a prior art printed circuit board assembly composed of a printed circuit board 12a and a circuit membrane 10a. The circuit membrane 10a has an extended ribbon cable 11a electrically connected to the printed circuit board 12a. The prior art printed circuit board 12a is electrically connected to the ribbon cable 11a through a connection stage 13a. The connection stage 13a is arranged on the printed circuit board 12a and the ribbon cable 11a is inserted into the connection stage 13a such that the circuit membrane 10a is electrically connected to the printed circuit board 12a. The use of connection stage 13a can achieve stable connection. However, the cost of the connection stage 13a is high and the assembling thereof is time consuming.
FIGS. 2 and 3 show another prior art printed circuit board assembly for keyboard. The keyboard has a flexible pad 15a on the cover plate 14a thereof. The ribbon cable 11a of the circuit membrane is sandwiched between the flexible pad 15a and the printed circuit board 12a. Moreover, the printed circuit board 12a is fixed to the flexible pad 15a by screwing two screws 16a such that the ribbon cable 11a of the circuit membrane is clamped between the cover plate 14a and the printed circuit board 12a. The electric contacts of the printed circuit board 12a are in contact with the electric contacts of the ribbon cable 11a of the circuit membrane. However, the screws 16 are generally screwed at both lateral sides of the printed circuit board 12a, the stress exerted on the printed circuit board 12a is uneven. The center part of the printed circuit board 12a is protuberant and the electric contacts of the printed circuit board 12a have poor contact with the electric contacts of the ribbon cable 11a. 
It is an object of the present invention to provide a printed circuit board assembly. After screws screw the both sides of the printed circuit board, the stress can be uniformly distributed. Therefore, the electric contacts of the printed circuit board are in firm contact with the electric contacts of the circuit membrane.
It is another object of the present invention to provide a printed circuit board assembly, which has simple structure and the cost and assembling time is saved.
To achieve the above object, the present invention provides a printed circuit board assembly comprises a circuit membrane, a printed circuit board, a cover plate and two screws.
The circuit membrane has an extended ribbon cable with a plurality of electric contacts. The printed circuit board has a plurality of electric contacts corresponding to the electric contacts of the circuit membrane. The cover plate has an arch-shaped bump formed thereon and the location thereof being corresponding to the electric contacts of the circuit membrane and the printed circuit board. The screws penetrate through both sides of the printed circuit board and are screwed to the cover plate, thus fixing the printed circuit board to the cover plate and clamping the ribbon cable between the cover plate and the printed circuit board. The electric contacts of the printed circuit board are in contact with the electric contacts of the circuit membrane.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which: